2.5 BIOLOGICAL MEMBRANES

Question 1

What is the fluid mosaic model of membranes

Answer 1

Fluid -phospholipid bilayer as phospholipids can move freely
Mosaic - extrinsic and intrinsic proteins, different shapes,size and positions

Question 2

What is the role of cholesterol

Answer 2

Reduces fluidity and makes bilayer more stable

Question 3

What is the role of glycolipids

Answer 3

Act as receptors for cell signalling

Cell recognition

Question 4

What is the function of an intrinsic glycoproteins

Answer 4

Receptors for drugs,hormones
Antigens
Cell adhesion
Involved in cell signalling

Question 5

Explain the function of intrinsic proteins in membranes

Answer 5

Channel proteins for passive diffusion of polar molecules and ions
Carrier proteins for facilitated diffusion and active transport

Question 6

Explain function within cells of membrane

Answer 6

Internal transport system
Selectively permeable to regulate passage of molecules into/out of organelles
Isolate organelles from cytoplasm for specific metabolic reactions
Form vesicles to transport between different areas of cells

Question 7

What is the function of the cell surface membrane

Answer 7

Isolates cytoplasm from extracellular environment
Regulate transport of substance
Involved in cell signalling/cell recognition

Question 8

What are 3 factors that affect membrane permeability

Answer 8

Temperature - high temperature denatures membrane protein/phospholipid molecules
pH- changes tertiary structure of membrane proteins
Solvent - may dissolve membrane

Question 9

PAG- how colorimetric can be used to investigate membrane permeability

Answer 9

Use plant tissue with soluble pigment in vacuole. Tonoplast and cell surface membrane disrupted =^permeabiliy=pigment diffuses into solution
Select colorimeter filter with complementary colour
Use distilled water to set colorimeter to 0
High absorbance/low transmission =more pigment in solution

Question 10

Define osmosis

Answer 10

When water diffuses across semi permeable membrane from an area of higher water potential to an area of lower water potential until a dynamic equilibrium is established

Question 11

What is water potential

Answer 11

Water pressure created by water molecules measured in kPa

Question 12

How does osmosis affect plant and animal cells

Answer 12

Into cell 
Plant -protoplast swells 
Animal -lysis 
Out of cell 
Plant -protoplast shrinks 
Animal - cremation

Question 13

Define Simple diffusion

Answer 13

Passive process -requires no energy from ATP hydrolysis
Net movement of small, lipid soluble molecules directly through a bilayer from an area of high concentration to an are of low concentration

Question 14

Define facilitated diffusion

Answer 14

Passive process
Specific channel or carrier proteins with complementary binding sites to transport large and/or polar molecules down a concentration gradient

Question 15

Explain how channel and carrier proteins work

Answer 15

Channel - hydrophilic channels bind to specific ions where one side of the protein closes and the other opens
Carrier - happens in passive process, AT, facilitated diffusion where it binds to complementary molecule and then change releases on the other side of the membrane

Question 16

Describe the process of active transport

Answer 16

Active process - requires ATP hydrolysis , releases phosphate group that binds to carrier protein-changes shape
Specific carrier protein transport it against the concentration gradient

Question 17

What is exocytosis and endocytosis

Answer 17

Active process
Involved in bulk transport
Membrane forms a vesicle
Vesicles fuse with cell surface phospholipid membrane

Question 18

What are 5 factors that affect rate of diffusion

Answer 18

Temperature
Diffusion distance
Surface area
Size of molecule

Question 19

What can affect cells

Answer 19

Affected by water potential of the surrounding soloution

Question 20

What happens in an animal cell where the surrounding solution is hypotonic (higher water potential)

Answer 20

Net movement of water molecules is into the cell

Cell burst

Question 21

If isotonic solution(same water potential) outside the animal cell

Answer 21

Water molecules pass into and out of cell in equal amounts

Cell stays the same

Question 22

Hypertonic solution(lower water potential)

Answer 22

Net movement of water molecules is out of the cell

Cell shrinks

Question 23

What is the net movement of plant cell in a hypotonic solution

Answer 23

Water into cell
Vacuole swells
Cell became turgid

Question 24

Net movement in an isotonic solution of plant

Answer 24

Water molecules move into cell in equal amounts

Cell stays the same

Question 25

What is the net movement of hypertonic solution in plant

Answer 25

Net movement of water is out of the cell

Cell becomes flaccid

Question 26

Describe how you would investigate the factor of temperature of cell permeability using a colorimeter

Answer 26

use beetroot; contains betalain dye; cut beetroot into small cubes; place in water at different temperatures; (at least) 5 different temperatures; sample water after set time ;
use filter in colorimeter; zero colorimeter ; (for each sample) record, absorbance / transmission;

Question 27

Describe the structure of a plasma(cell surface) membrane

Answer 27

Phospholipid bilayer containing scattered proteins
Hydrophilic head facing outwards
Hydrophobic tails facing inwards

Question 28

Outline the roles of membranes within cells

Answer 28

Compartmentalisation

Allows formations of concentration gradient

Question 29

Identify 2 problems with method of transpiration using bag

Answer 29

Some water vapour not condense
Record mass
Water vapour might escape
Use elastic band

Question 30

Which protein is needed to transport large polar molecules

Answer 30

Carrier protein